There are literally thousands of inventions relating to unique structures for presser feet and all work satisfactorily in the environment in which they are designed to operate. However, a problem exists which does not appear to have been addressed by the industry. It is that strings, foam rubber, and other types of obstructions are sometimes present on the upper surface of materials to be sewn together and where they project above the upper surface of the material to be sewn, they can be caught in the gap between forwardly projecting sole plates on presser feet.
This invention came about in an industry which sews fabric and plastic covers for automobile seats. During the sewing operation, there are certain parts of the cover which have a thread extension called a "chain off" which extend one to three inches beyond the edge of the material of the seat cover. The "chain off" prevents the unravelling of the sewn area which occurs if the thread extensions are cut off too close to the end of the material. This "chain off" extension of thread often projects above the surfaces to be sewn. When a transversely extending thread pattern is required to sew the edges of two parts of the seat together, the thread extensions tend to tangle in the presser foot.
The factory where this invention was conceived has dozens of employees sewing automobile seat covers together and where the thread extension accidentally becomes entangled in the presser foot and the threaded, reciprocating needle, the machine must be closed down and the apparatus disentangled before sewing can be resumed.
A test was conducted over a period of time and on average each sewing machine did about 100 seats a day. On average, 71 thread tangles occurred in each machine. After the shield of this invention was attached to the presser feet of the machines, the average entanglement was reduced to three per day per worker for an eight hour shift.
In reviewing the subject matter of unique structure for presser feet, a patent to Hill, U.S. Pat. No. 2,699,743, shows a presser foot having a pair of transversely extending gaps in an upstream extension of the presser foot which guides a set of folds to be sewn together at the edge of a fabric panel. The needle reciprocates vertically through a closed loop hole in the presser foot.
A patent to Egert, U.S. Pat. No. 3,195,486, discloses a reciprocating needle operating in a closed loop on the presser foot. A forwardly extending guide 105, 106, 107 serves to guide the elements to be sewn toward the needle area.
A patent to Van Amburg, U.S. Pat. No. 3,858,539, discloses in FIG. 3 a triangular or cone-shaped deflector 24 upstream of a needle which is confined within a closed loop within the presser foot. The triangular-shaped deflector 24 is structured cooperatively with a pair of side channels which serve collectively to guide elements to be sewn in a converging pattern and funneled toward the needle.
A patent to Kaminski, U.S. Pat. No. 3,875,878, looks very much like the invention described herein except that its structure is in a combination which is intended to prevent upward movement of the workpiece from the needle plate, see column 57, lines 27-29. One thing the patent structure shows and describes in relation to the presser foot is a curved side portion 91 which prevents portions of the workpiece from accidentally being pushed into the path of the needle 84, see particularly column 5, lines 3-36 and 38-40. What it does not disclose is a combination of two sole plates with an L-shaped shield attached to the presser foot.